1. Field of the Invention
The invention relates to a DC-DC converter adapted to interconnecting different DC systems with different voltage levels.
2. Description of the Related Art
A conventional method for interconnecting multiple DC systems with different voltage levels is to connect each two DC systems via a two-port DC-DC converter. However, this method requires a large number of two-port DC-DC converters, and features high cost and great power loss. Another method is to use a multiport DC-DC converter.
Typically, the multiport DC-DC converter employs an inductor-capacitor-inductor (LCL) circuit, or employs a multiport high-frequency transformer. A remarkable feature of the multiport DC-DC converters employing either the LCL circuit or the multiport high-frequency transformer is that there is no direct connection between DC sides of interconnected DC systems. As such, it is impossible for the multiport DC-DC converter to fully utilize existing DC voltage of all DC systems, power can only be transferred only after DC-AC-DC conversion, and overall power rating of the converter is twice an interconnected power rating, which increases cost of the converters and an AC link, and causes great power loss.
Although there is a stereoscopic DC-DC converter fully utilizing existing DC voltage of low-voltage DC systems by connecting three converters in series, the scheme can only connect two DC systems with different voltage level, while cannot connect three or more DC systems with different voltage levels, and does not tell how to determine rated voltage and rated power of each converter in the stereoscopic DC-DC converter containing more than three converters.